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L’objectiu principal d’aquest estudi fou la quantificació de l’efecte de diferents tipus de conreu del sòl i tipus i dosis de fertilització nitrogenada sobre l’emissió de gasos d’efecte hivernacle (CH4, CO2 i N2O) del sòl a l’atmosfera i l’agregació del sòl com a mecanisme de protecció del carboni orgànic en agroecosistemes de secà semiàrid Mediterranis. Per tal d’assolir aquest objectiu es varen plantejar cinc camps experimentals on s’hi comparaven sistemes de conreu (sembra directa i conreu intensiu) i tipus (minerals i orgànics) i dosis de fertilitzants nitrogenats, localitzats al centre i l’est de la vall de l’Ebre. A Agramunt (Lleida, establert l’any 1996) i Senés de Alcubierre (Huesca, establert l’any 2010) s’hi van quantificar les emissions de CO2, CH4 i N2O al llarg de dos i tres anys, respectivament, els estocs de C i N orgànics del sòl i el rendiment de collita i es va calcular l’emissió d’equivalents de CO2 per kg de gra produït. Alhora, a Agramunt es va determinar la proporció de macroagregats i microagregats estables a l’aigua i la concentració de C d’ambdós així com la d’altres fraccions del sòl. D’altra banda, en un altre experiment a Agramunt es va establir una cronoseqüència de sembra directa de cinc fases amb 0, 1, 4, 11 i 20 anys, en les que es va determinar la distribució d’agregats estables a l’aigua i tamisats en sec i la seva concentració de C orgànic. A St. Martí Sesgueioles (Barcelona, establert l’any 2007) s’hi van comparar dosis creixents de fertilitzant mineral en un maneig del sòl en sembra directa. A Conill (Barcelona, establert l’any 2008) es va estudiar l’aplicació de purí porcí a dos dosis de N, gallinassa i un tractament control també sota sembra directa. En ambdós experiments es va realitzar un seguiment de la dinàmica temporal de l’agregació del sòl, la protecció del carboni en els agregats i el carboni de la biomassa microbiana durant dos campanyes de cultiu. Finalment, es va realitzar una incubació de macroagregats per a observar l’impacte del tipus de conreu i del tipus de fertilització (mineral i orgànica amb purí porcí) sobre la producció de CH4, CO2 i N2O. En general, els sistemes de conreu i el maneig de la fertilització nitrogenada van afectar les emissions de gasos d’efecte hivernacle del sòl a l’atmosfera i, en el cas del conreu, l’estabilització física del carboni orgànic del sòl. Així, per als sistemes de conreu, en l’experiment de curt termini, sota sembra directa es van generar unes majors emissions de N2O i CO2 i una menor oxidació del CH4 que en conreu intensiu. No obstant, al comparar-los a llarg termini, ambdós sistemes de conreu van presentar la mateixa emissió de N2O i la oxidació del CH4 va ser major en sembra directa, fets que també es van observar a l’incubar els macroagregats. Alhora, a l’augmentar el nombre d’anys sota sembra directa, el sòl va presentar una major proporció de macroagregats estables i una major formació de microagregats d’elevada concentració de C. Pel que fa a l’impacte de la fertilització nitrogenada sobre l’emissió de gasos d’efecte hivernacle, l’aplicació de dosis creixents de N tan orgànic com mineral va provocar un augment de la emissió de N2O del sòl. En canvi, per a una mateixa dosi, aquests dos tipus de fertilitzant van emetre una quantitat de N2O similar. D’altra banda, la fertilització nitrogenada mineral no va millorar la protecció del C en els agregats del sòl mentre que la orgànica només va promoure un lleu increment en l’estabilitat d’aquests. Als secans semiàrids Mediterranis, la combinació de l’ús de la sembra directa i la fertilització amb dosis mitjanes de purí porcí és una estratègia de maneig òptima ja que minimitza les emissions de gases d’efecte hivernacle i manté la productivitat del cultiu. Alhora, ambdues pràctiques milloren l’estabilitat dels agregats, maximitzant la quantitat de carboni orgànic segrestat i millorant l’estat estructural del sòl., El objetivo principal de este estudio fue cuantificar el efecto de diferentes tipos de laboreo del suelo y dosis de fertilización nitrogenada sobre la emisión de gases de efecto invernadero (CH4, CO2 y N2O) del suelo a la atmosfera y la agregación del suelo como mecanismo de protección del carbono orgánico en agroecosistemas de secano semiárido Mediterráneo. Para alcanzar este objetivo se plantearon cinco campos experimentales en los que se comparaban sistemas de laboreo (siembra directa y laboreo intensivo) y tipos (minerales y orgánicos) y dosis de fertilizantes nitrogenados, localizados en el centro y el este del valle del Ebro. En Agramunt (Lleida, establecido el año 1996) y Senés de Alcubierre (Huesca, establecido el año 2010) se cuantificaron las emisiones de CO2, CH4 y N2O a lo largo de dos y tres años, respectivamente, los stocks de C y N orgánicos del suelo y el rendimiento de cosecha y se calculó la emisión de equivalentes de CO2 per kg de grano producido. Además, en Agramunt se determinó la proporción de macroagregados y microagregados estables al agua y la concentración de C de ambos así como otras fracciones del suelo. Por otro lado, en otro experimento en Agramunt se estableció una cronosecuencia de siembra directa de cinco fases con 0, 1, 4, 11 y 20 años, en las que se determinó la distribución de agregados estables al agua y tamizados en seco y su concentración de C orgánico. En St. Martí Sesgueioles (Barcelona, establecido el año 2007) se compararon dosis crecientes de fertilizantes mineral en un manejo del suelo en siembra directa. En Conill (Barcelona, establecido el año 2008) se estudió la aplicación de purín a dos dosis de N, gallinaza y un tratamiento control también bajo siembra directa. En ambos experimentos se realizó un seguimiento de la dinámica temporal de la agregación del suelo, la protección del carbono en los agregados y el carbono de la biomasa microbiana durante dos campañas de cultivo. Finalmente, se realizó una incubación de macroagregados para observar el impacto del tipo de laboreo y del tipo de fertilización (mineral y orgánica con purín porcino) sobre la producción de CH4, CO2 y N2O. En general, los sistemas de laboreo y el manejo de la fertilización nitrogenada afectaron las emisiones de gases de efecto invernadero del suelo a la atmosfera y, en el caso del laboreo, la estabilización física del carbono orgánico del suelo. Así, para los sistemas de laboreo, en el experimento de corto plazo, bajo siembra directa se generaron unas mayores emisiones de N2O y CO2 y una menor oxidación del CH4 que en laboreo intensivo. No obstante, al compararlos a largo plazo, ambos sistemas de laboreo presentaron la misma emisión de N2O y la oxidación de CH4 fue mayor en siembra directa, hechos que también se observaron al incubar los macroagregados. Además, al aumentar el número de años bajo siembra directa, el suelo presentó una mayor proporción de macroagregados estables y una mayor formación de microagregados de elevada concentración de C. Por lo que respecta al impacto de la fertilización nitrogenada sobre la emisión de gases de efecto invernadero, la aplicación de dosis crecientes de N tanto orgánico como mineral provocó un aumento de la emisión de N2O del suelo. En cambio, para una misma dosis, estos dos tipos de fertilizante emitieron una cantidad de N2O similar. Por otro lado, la fertilización nitrogenada mineral no mejoró la protección del C en los agregados del suelo mientras que la orgánica solo promovió un leve incremento en la estabilidad de éstos. En los secanos semiáridos Mediterráneos, la combinación del uso de la siembra directa y la fertilización con dosis medias de purín porcino es una estrategia de manejo óptima ya que minimiza las emisiones de gases de efecto invernadero y mantiene la productividad del cultivo. Además, ambas prácticas mejoran la estabilidad de los agregados, maximizando la cantidad de carbono orgánico secuestrado y mejorando el estado estructural del suelo., The main objective of this study was the quantification of the effects of different types of soil tillage and types and rates of nitrogen fertilization on the emission of soil greenhouse gases (CH4, CO2 and N2O) to the atmosphere and the soil aggregation as an organic carbon protection mechanism in the dryland semiarid Mediterranean agroecosystems. In order to achieve that objective five experimental fields were established comparing different tillage systems (notillage and intensive tillage) and types (mineral and organic) and rates of nitrogen fertilizers, localized in the center and East of the Ebro Valley. In Agramunt (Lleida, established in 1996) and Senés de Alcubierre (Huesca, established in 2010) CO2, CH4 and N2O emissions were quantified during two and three years, respectively. Soil organic C and N stocks, crop yield and the emission of CO2 equivalents per kg of grain produced were also determined. Moreover, in Agramunt, water-stable macroaggregates, microaggregates within macroaggregates and their C concentration and other different soil fractions were quantified. In turn, in another experiment in Agramunt a no-tillage chronosequence with 0, 1, 4, 11, 20 years was established and the water-stable and dry-sieved aggregates distributions and their C concentration were determined. In St. Martí Sesgueioles (Barcelona, established in 2007) increasing rates of mineral fertilizer under no-tillage were compared. In Conill (Barcelona, established in 2008) the application of pig slurry at two N rates, poultry manure and a control treatment under a no-tillage management were studied. In both experiments the soil aggregation dynamics, the C protection within aggregates and their C concentration and the microbial biomass carbon were analyzed during two cropping seasons. Finally, an incubation of macroaggregates was carried out in order to study the impact of the type of tillage and fertilizer (mineral and organic with pig slurry) on the production of CH4, CO2 and N2O. In general, tillage systems and nitrogen fertilizer management affected the emissions of soil greenhouse gases to the atmosphere while tillage also impacted the physical stabilization of organic carbon. In the case of tillage system, in the short-term experiment, greater N2O and CO2 emissions and lower CH4 oxidation were observed. However, in the long-term, both tillage systems presented the same N2O emission and the CH4 oxidation was greater under no-tillage, aspects that were also observed in the macroaggregate incubation. Moreover, the soil presented a greater proportion of water-stable macroaggregates and greater C-enriched microaggregates within those macroaggregates when increasing the number of years under no-tillage. In the case of the impact of the nitrogen fertilization on the greenhouse gases emission, the application of increasing N rates by both organic and mineral sources increased the soil N2O emission. As a difference, for a given N rate, similar amount of soil N2O was quantified for both fertilizer types. The mineral nitrogen fertilization did not improve the C protection within soil aggregates while the organic fertilization caused a low increase in their stability. In the dryland semiarid agroecosystems of the Mediterranean, the combination of no-tillage and fertilization with medium N rates of pig slurry is an optimum strategy in terms of greenhouse gases minimization and maintenance of crop productivity. Moreover, both practices improve the aggregate stability maximizing the amount of organic carbon protected and improving soil structure.

30 Pags., 6 Tabls., 3 Figs. The definitive version is available at: http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1475-2743, In rainfed semi-arid agroecosystems, soil organic carbon (SOC) may increase with the adoption of alternative tillage systems (e.g. no-tillage, NT). This study evaluated the effect of two tillage systems (conventional tillage, CT vs. NT) on total SOC content, SOC concentration, water stable aggregate-size distribution and aggregate carbon concentration from 0 to 40 cm soil depth. Three tillage experiments were chosen, all located in northeast Spain and using contrasting tillage types but with different lengths of time since their establishment (20, 17, and 1-yr). In the two fields with mouldboard ploughing as CT, NT sequestered more SOC in the 0–5 cm layer compared with CT. However, despite there being no significant differences, SOC tended to accumulate under CT compared with NT in the 20–30 and 30–40 cm depths in the AG-17 field with 25–50% higher SOC content in CT compared with NT. Greater amounts of large and small macroaggregates under NT compared with CT were measured at 0–5 cm depth in AG-17 and at 5–10 cm in both AG-1 and AG-17. Differences in macroaggregate C concentration between tillage treatments were only found in the AG-17 field at the soil surface with 19.5 and 11.6 g C/kg macroaggregates in NT and CT, respectively. After 17 yr of experiment, CT with mouldboard ploughing resulted in a greater total SOC concentration and macroaggregate C concentration below 20 cm depth, but similar macroaggregate content compared with NT. This study emphasizes the need for adopting whole-soil profile approaches when studying the suitability of NT versus CT for SOC sequestration and CO2 offsetting., This research was supported by the Comision Interministerial de Ciencia y Tecnologia of Spain (AGL 2004-07763-C02-02 and AGL 2007-66320-C02). The first author was awarded with a fellowship by the Spanish Ministry of Education.

42 Pags.- 5 Tabls.- 4 Figs. © 2020 The Authors. Soil Science Society of America Journal © 2020 Soil Science Society of America, The aim of this study was to evaluate the impact of 21 years of tillage and N fertilization and the conversion from a rainfed to an irrigated cropping system on soil organic C (SOC). The study was carried out in northeastern Spain in a long‐term tillage and N rate field experiment established in 1996 under barley rainfed conditions, which in 2015 was converted into irrigation with corn. Three types of tillage (conventional tillage, CT; reduced tillage, RT; no‐tillage, NT) and three mineral N fertilization rates (0, 60, and 120 kg N ha−1 under barley, and 0, 200, and 400 kg N ha−1 under corn) were compared. Annual C‐inputs as aboveground crop residues and annual SOC sequestration rate (∆SOCrate) (0–40 cm depth) were calculated in three different periods (P1, P2 and P3) under rainfed (‐R) and irrigated (‐I) conditions (P1‐R, from 1996 to 2009; P2‐R, from 2009 to 2015; P3‐I, from 2015 to 2017). At the end of P3‐I, particulate organic C (POC) was measured from the 0–5, 5–10, 10–20, 20–30, and 30–40 cm depths. Averaged over all treatments, ∆SOCrate was 492, 222, and 969 kg C ha−1 yr−1 for P1‐R, P2‐R, and P3‐I, respectively. In P1‐R and P3‐I, C‐input explained 70% of the variability of ∆SOCrate. In P1‐R, ∆SOCrate followed the order NT > RT > CT, while for N rate, order was high > medium > 0. In P3‐I at the highest N rate, ∆SOCrate followed the order NT > RT > CT. In P2‐R, ∆SOCrate did not show differences between tillage and/or N rate treatments. The increase in SOC after conversion from a rainfed to an irrigation system was mainly explained by POC, which was increased by 75% compared to the previous rainfed period. The modification of the cropping system through the introduction of irrigation and adequate crop management practices under no‐tillage and adjusted N fertilizer rates can contribute to the sequestration of large amounts of atmospheric CO2., This research work was financially supported by the Ministerio de Economía y Competitividad of Spain (project AGL2013-49062-C4-1-R; PhD fellowship BES‐2014‐070039). DPB received a Juan de la Cierva postdoctoral grant from the Ministerio de Economía y Competitividad of Spain (IJCI-2016-27784) and is Ramón y Cajal fellow (RYC2018-024536-I) of the Ministerio de Ciencia, Innovacion y Universidades.

28 Pags.- 3 Figs., Major constraints to rainfed production systems in the world’s drylands include low and highly variable rainfall, nutrient deficiencies and land degradation by wind and water erosion. Although the same principles to cope with these limitations could be in theory applied to all dryland situations, there is no a universal recipe for sustainable dryland agriculture. In this chapter, the authors recall some of the challenges that have been identified for semiarid rainfed farming systems, namely soil conservation, water use efficiency, nutrient use efficiency and climate change mitigation, as well as some sustainable cropping and management strategies that have been formulated and recommended to address them appropriately. To this end, the authors provide examples supporting those practices mainly from semiarid Mediterranean agroecosystems. Among all the strategies discussed in this Chapter, and despite their limitations, the maintenance of a protective crop residue cover and the reduction of tillage operations appear to be the simplest technological options not only to control soil erosion but also to improve water and nutrient use efficiency and mitigate greenhouse gas emissions. The authors conclude that sustainable agricultural management in drylands should be primarily based on conservation agriculture practices and associated local-based crop residue management systems.

In irrigated Mediterranean conditions there is a lack of knowledge about the best combination of tillage and N fertilization practices to reduce soil nitrous oxide (N2O) emissions while maintaining maize productivity. The aim of this work was to investigate the effects of different soil management practices and synthetic N fertilization rates on soil N2O emissions and their relationship with maize grain yield to determine the best management system to reduce yield-scaled N2O emissions (YSNE) in a semiarid area recently converted to irrigation under Mediterranean conditions. A long-term tillage and N rate field experiment established in 1996 under barley (Hordeum vulgare L.) rainfed conditions, was converted to irrigated maize (Zea mays L.) in 2015. After the transformation to irrigation, the field experiment maintained the same tillage treatments and N fertilization rates. Three types of tillage (conventional tillage, CT; reduced tillage, RT; no-tillage, NT) and three mineral N fertilization rates (0, 200, 400 kg N ha−1) were compared during three years (2015–2017) in a randomized block design with three replications. Soil N2O emissions, water-filled pore space, soil temperature, mineral N content (as NH4+ and NO3−), denitrification potential and maize grain yield and above-ground N uptake were quantified. Moreover, the emission factor (EF) and YSNE were calculated. The results showed that the combination of NT and the highest rate of N fertilization led to greater N2O emissions. Furthermore, the lowest N2O fluxes were observed in CT when WFPS was below 40% and the highest N2O fluxes were seen in NT when WFPS was above 60% coinciding with the greatest denitrification potential. Cumulative N2O emissions in 2017 and 2015 followed the order 400 > 200 > 0 kg N ha−1, while in 2016, rate of 400 and 200 kg N ha−1 showed greater cumulative N2O emission compared to the control. Only RT showed differences between growing seasons on cumulative N2O emissions, with greater values in 2017 compared to 2015, and intermediate values in 2016. In all treatments, the N2O EF was much lower than the default IPCC emission factor (1%). NT and RT increased the grain production compared to CT which was affected by severe soil crusting causing water deficit. Likewise, N fertilizer treatments significantly affected the YSNE, increasing with increasing fertilizer N application rate in the first year of study. Our data show that the use of NT or RT does not lead to more yield-scaled N2O emissions than CT in Mediterranean agroecosystems recently converted to irrigation., This research work was financially supported by the Ministerio de Economía y Competitividad of Spain (project AGL2013-49062-C4-1-R; PhD fellowship BES‐2014‐070039). DPB received a Juan de la Cierva postdoctoral grant from the Ministerio de Economía y Competitividad of Spain (IJCI-2016-27784).

11 Pags.- 2 Tabls.- 7 Figs., Mediterranean rainfed areas are transformed into irrigation to stabilize or increase crop yields. The gradual occupation of irrigation leads to an increase in nitrogen use and intensity of tillage. The aim of this work was to evaluate the combined impact of tillage systems and mineral N fertilization rates on maize grain yield, water and nitrogen use efficiencies (WUE and NUE) under Mediterranean irrigated conditions. The study was carried out in NE Spain during three maize growing seasons (i.e. years 2015, 2016 and 2017). A long-term (LTE) tillage and N rate field experiment established in 1996 under rainfed conditions was transformed into irrigation with maize (Zea mays L.) monocrop as cropping system in 2015. Three types of tillage (conventional tillage, CT; reduced tillage, RT; no-tillage, NT) and three mineral N fertilization rates (0, 200, 400 kg N ha−1) were compared. In 2015, an adjacent experiment (short-term experiment, STE) with the same layout was set up in an area previously managed under long-term rainfed NT for the last 21 years. In the long-term tillage and N fertilization combination (LTE), the reduction of tillage (NT and RT) led to greater grain yield when applying 200 and 400 kg N ha−1 compared to the use of the same rates under CT. Differently, in the sort-term experiment with preceding NT (STE), tillage systems did not influence grain yields, while N application led to greater yields than the control (0 kg N ha−1). In both situations (LTE and STE), NT and RT enhanced soil water content before planting leading to greater crop growth compared to CT. The lack of available water under CT caused lower maize stover, yield, and yield components in LTE and, therefore, lower WUEB (for biomass) and WUEY (for yield). In LTE, the use of long-term CT led to a significant accumulation of nitrate compared to NT. Differently, in the STE, soil nitrate content did not show differences between tillage systems. In the LTE, water and N were used more efficiently to produce aboveground biomass and grain yield in RT and NT. Our study shows that in Mediterranean agroecosystems transformed into irrigation the use of NT and RT with medium rates of N leads to greater maize yield, WUE and NUE than the traditional management based on CT with high rates of mineral N. In rainfed areas with long-term history of no-till, this soil management system can be successfully maintained if transformed into irrigation., This research work was financially supported by the Ministerio de Economía y Competitividad of Spain (project AGL2013-49062-C4-1-R; PhD fellowship BES‐2014‐070039). DPB received a Juan de la Cierva postdoctoral grant from the Ministerio de Economía y Competitividad of Spain (IJCI-2016-27784).

8 Pags.- 2 Tabls.- 5 Figs., In newly irrigated Mediterranean agroecosystems, the combined effect of tillage and N fertilization on soil carbon dioxide (CO2) and methane (CH4) fluxes is at present poorly understood. The goal of this study was to quantify both soil CO2 and CH4 emissions as well as crop performance under different tillage systems and N fertilization rates during three maize (Zea mays L.) growing seasons (2015–2017) in a semiarid area converted to irrigated. Three types of tillage (conventional tillage, CT, reduced tillage, RT, and no-tillage, NT) and three mineral N fertilization rates (0, 200, and 400 kg N ha−1) were compared in a randomized block design with three replications. Weekly soil CO2 and CH4 emissions, soil temperature and gravimetric moisture were measured. Moreover, maize above-ground biomass, grain yield, and above-ground C-inputs were quantified. Carbon dioxide emissions ranged from 173 to 4378 mg CO2-C m-2 d-1. No-tillage showed a greater mean soil CO2 flux than CT when applying the highest rate of N (400 kg N ha-1). Although some emissions of CH4 were observed, all treatments acted as net CH4 sinks during most of the experimental period. A linear multiple relationship between soil CO2 fluxes and soil gravimetric moisture (0–5 cm depth) and temperature (10 cm depth) were found. In the 2015 growing season, greater cumulative CO2 emissions were found under NT and RT compared with CT, while in 2016 N T showed the highest values compared to CT with intermediate values in RT. Differently, in 2017 no differences between tillage systems were found. When applying N fertilizer, NT and RT increased maize grain production and above-ground C-inputs compared to CT, since a severe soil crusting occurred in this last, which caused crop water deficit. The results suggest that tillage intensity and N fertilization rate reduction can increase maize biomass production and yield which leads to greater C-input that returns to the soil., This research work was financially supported by the Ministerio de Economía y Competitividad of Spain (project AGL2013-49062-C4-1-R; PhD fellowship BES‐2014‐070039). DPB received a Juan de la Cierva postdoctoral grant from the Ministerio de Economía y Competitividad of Spain (IJCI-2016-27784).

49 Pags.- 10 Figs.- 6 Tabls. The definitive version is available at: https://www.sciencedirect.com/science/journal/01671987, Irrigation as well as soil tillage management are considered two possible strategies to reduce carbon dioxide (CO2) and methane (CH4) emissions from the soil in Mediterranean agroecosystems. The objective of this work was to assess the impact of the irrigation system (i.e. flood, F; and sprinkler, S) and the soil tillage system (i.e. conventional tillage, CT; no-tillage maintaining the maize stover, NTr; and no-tillage removing the maize stover, NT) on CO2 and CH4 emissions from the soil during three growing seasons (2015, 2016 and 2017) and two fallow periods between growing seasons (15–16 fallow and 16–17 fallow) in a maize (Zea mays L.) monoculture system. Soil temperature and water-filled pore space (WFPS) had a great influence on daily soil CO2 fluxes but not on daily soil CH4 fluxes. In all tillage-irrigation treatments, daily soil CO2 fluxes showed an increase with soil temperature, being this increment greater when soil temperature was above 15 °C in coincidence with the maize plant growth. In contrast, soil WFPS differently affected daily soil CO2 fluxes depending on the irrigation system. Under S irrigation, daily soil CO2 fluxes increased with soil WFPS, whereas under F irrigation a threshold value of 60% WFPS was found, with a positive or negative effect on CO2 fluxes for values below or above this threshold value, respectively. Over the three maize growing seasons, CT-S presented the greatest cumulative soil CO2 emissions with a seasonal average value of 3.28 Mg CO2-C ha−1. In contrast, for the same period, NTr-S cumulative soil CO2 emissions were up to 42% lower than the CT-S cumulative soil CO2 emissions. Cumulative CH4 emissions were only affected by soil tillage during the 16–17 fallow period, resulting both NTr and NT in greater net CH4 uptake compared with CT. This work highlights the importance of irrigation and soil tillage systems as key agricultural practices to minimize soil CO2 and CH4 emissions under Mediterranean conditions., Samuel Franco-Luesma was awarded a FPI fellowship by the Ministry of Science, Innovation and Universities (MICINN) of Spain (ref. BES-2014-069175). Daniel Plaza-Bonilla was awarded a Juan de la Cierva postdoctoral grant by MICINN (refs. FJCI-2014-19570; IJCI-2016-27784). This research was supported by a MICINN grant (ref. AGL2013-49062-C4-4-R).

47 Pags.- 4 Tabls- 5 Figs. The definitive version is available at: https://www.sciencedirect.com/science/journal/01678809, There is a strong need to identify agricultural management practices that maintain agronomic productivity while diminishing soil N2O emissions. The yield-scaled N2O emissions (YSNE) indicator can help to evaluate the adequacy of a given agricultural practice under both aspects. Long-term (18-yr) soil water and mineral N dynamics, crop biomass and yields, and 2011–2012 soil N2O emissions and ancillary variables were measured on barley (Hordeum vulgare L.) production in a tillage (conventional tillage, CT; no-tillage, NT) and N rate (0, 60 and 120 kg N ha−1) combination under rainfed Mediterranean conditions (NE Spain). Once evaluated, the STICS soil-crop model was used to simulate the 18-yr soil N2O emissions of each tillage system under increasing N rates (0, 30, 60, 90 and 120 kg N ha−1) in order to identify optimum management to reduce YSNE, being initialized with observed data. Cropping season precipitation was highly variable during the experiment, being a key regulating mechanism for crop yields and simulated soil N2O emissions. Crop yield under NT with N outperformed CT in 11 years. STICS performed reasonably well when simulating cumulative N2O emissions and ancillary variables with model efficiencies greater than 0.5. The 18-yr average simulated cumulative N2O emissions were 0.50, 0.82 and 1.09 kg N2O-N ha−1 yr−1 for CT-0, CT-60 and CT-120, respectively, and they were 0.53, 0.92 and 1.19 kg N2O-N ha−1 yr−1 for their counterparts under NT. These averages mask a large variability between years, according to precipitation. The 18-yr mean yield-scaled N2O emissions were 2.8–3.3 times lower under NT, compared to the corresponding CT treatments. Under CT, N application would increase YSNE in most years while YSNE would be more resilient to the application of increasing N rates under NT. Our work demonstrates that in rainfed Mediterranean systems NT is a win-win strategy for the equilibrium between agricultural productivity and low soil N2O emissions., This work was supported by the Comisión Interministerial de Ciencia y Tecnología of Spain (Project Grants AGL 2010-22050-C03-01/02 and AGL2013-49062-C4-1/4-R). DPB received a “Juan de la Cierva-Formación” postdoctoral grant from the Ministerio de Economía y Competitividad of Spain (ref. FJCI-2014-19570).